This invention relates to a vacuum chamber for a superconducting apparatus for producing synchrotron orbital radiation (hereinafter abbreviated as SOR). More particularly, it relates to a vacuum chamber which can be easily installed and removed from a bending magnet of a superconducting SOR apparatus.
Synchrotron orbital radiation is a form of electromagnetic energy which is emitted by charged particles in circular motion at relativistic speeds. It is given off in a continuous spectrum that extends from radio wavelengths through visible light into X-rays. Because of its high intensity, high degree of collimation, broad bandwidth, high polarization, and other properties, it is ideal for a large variety of applications in experimental science and technology.
FIG. 1 illustrates a conventional SOR storage ring 100. The storage ring 100 comprises a loop-shaped main vacuum chamber 1 through which a beam of charged particles (typically an electron beam) passes. A plurality of bending magnets 3 for bending the beam of charged particles are disposed at intervals along the main vacuum chamber 1. When the beam of charged particless is bent by the bending magnets 3, it emits SOR radiation 4 in a direction which is tangential to the orbit of the beam. This radiation 4 is removed from the main vacuum chamber 1 through a plurality of SOR vacuum chambers 2 which open onto the inside of the main vacuum chamber 1 at each of the bending magnets 3. A beam of charged particles 6 at relativistic speeds can be injected into the main vacuum chamber 1 via an incident beam vacuum chamber 5 which opens onto the inside of the main vacuumm chamber 1. The beam 6 is then accelerated and kept orbitting around the main vacuum chamber 1 by unillustrated electromagnets. In order to increase the strength of the SOR 4 which is emitted by the beam of charged particles and to prolong the life-span of the beam which is stored within the storage ring 100, it is important that an extremely high vacuum be maintained inside the main vacuum chamber 1, the SOR vacuum chamber 2, and the incident beam vacuum chamber 5 so that there will be no gas molecules or ions with the vacuum chambers which the beam of charged particles can collide with.
FIG. 2 illustrates the structure of a conventional vacuum chamber 10 for use in a bending magnet 3 for a storage ring 100 of this type, as described in a report entitled "Design of UVSOR Storage Ring", published by the Institute for Molecular Science (UVSOR-9, December, 1982, page 57, in Japanese). This vacuum chamber 10 comprises a main chamber 11 and an SOR chamber 12 which opens onto the inside of the main chamber 11. A beam of charged particles passes through the center of the main chamber 11, while the SOR chamber 12 is positioned such that SOR which is emitted by the beam will pass therethrough. Each end of the main chamber 11 has a connecting flange 14 formed thereon, while the outer end of the SOR chamber 12 has a similar flange 15 formed thereon. The main chamber 11 includes a built-in pump 13. In the figure, the center line 16 indicates the center line of a beam of charged particles passing through the main chamber 11. The main chamber 11 constitutes a portion of the main vacuum chamber 1 of FIG. 1, and the SOR chamber 12 constitutes a portion of the SOR vacuum chamber 2 of the same figure.
A vacuum chamber 10 of this type is normally installed in a conventional bending magnet 3 in the manner shown in FIGS. 3-5. A conventional bending magnet 3 comprises two sets of exciting coils 3a which are wrapped around the poles of a C-shaped iron core 3b. The vacuum chamber 10 is inserted into the air gap between the poles of the core 3b with the flanges 14 and 15 disposed completely outside of the core 3b. Although the flanges 14 and 15 have a diameter which is larger than the height of the gap between the poles of the core 3b, since there are no obstructions in the gap, the vacuum chamber 10 can be easily installed and removed from the bending magnet 3.
However, in the case of an SOR apparatus which employs superconducting electromagnets as bending magnets, the installation and removal of a conventional vacuum chamber can be extremely troublesome. Japanese Patent Application No. 61-28450, of which U.S. Pat. No. 4,737,727 is a counterpart, discloses a superconducting SOR apparatus which employs a superconducting bending magnet 20 of the type illustrated in FIG. 6. The superconducting bending magnet 20 comprises two parallel vacuum tanks 21 in which vacuums are maintained, each of the tans 21 housing a superconducting electromagnetic coil. The upper vacuum tank 21 is supported on the lower one by four support members 22. Vacuums are maintained inside each of the support members 22, and the upper and lower vacuum tanks 21 communicate with one another through the centers of the support members 22. The support members 22 contain structural members made of stainless steel or the like which are maintained at a low temperature and which mechanically support the superconducting coils within the upper and lower vacuum tanks 21. The structural members must be able to withstand electromagnetic forces on the order of several hundred tons which act on the superconducting coils during operation of the SOR apparatus so as to rigidly support the superconducting coils. Liquid helium and liquid nitrogen for cooling the superconducting coils are introduced into the vacuum tanks 21 via intake ports 23 which are supported by a tower 24 which is mounted atop the upper vacuum tank 21. The tower 24 also supports terminals for various electronic instrumentation.
With this type of superconducting bending magnet 20, if a conventional vacuum chamber 10 is installed therein in a manner analogous to that shown in FIG. 3 with the flanges 14 and 15 disposed outside of the bending magnet 20, the support members 22 prevent the vacuum chamber 10 from being easily inserted or removed from the bending magnet 20. Namely, because of the length of the main chamber 11 and the large diameter of the flanges 14 and 15, which is larger than the height of the gap betwen the vacuum tanks 21, it is necessary to partially disassemble the bending magnet 20 in order to insert or remove the vacuum chamber 10 from between the vacuum tanks 21. Because of the far lower pressure which must be maintained in the vacuum chamber 10 (at most 1.times.10.sup.-9 torr in the vacuum chamber 10 vs about 1.times.10.sup.-6 torr in the vacuum tanks 21), the vacuum chamber 10 is more prone to leaks and requires more frequent repair or replacement than the vacuum tanks 21. Nevertheless, with the conventional structure, it is necessary to disassemble the latter in order to service the former.